The prevalence of early childhood dental caries (ECC) has risen to 27% of the 14.6 million US children aged 2-5 years old. Direct costs to treat a child with ECC range from $408 to over $6000, if general anesthesia is used. Recent longitudinal studies find high rates of ECC among children whose teeth have developmental defects of enamel or DDE. Enamel hypoplasia (EH) is a DDE characterized by an area of less enamel that can harbor bacteria for dental caries. In animal models, EH is caused by the lack of, or the inability to utilize vitamin D (vitD). This is consistent with human EH observed in the permanent teeth of children with vitD- deficient rickets (lack of vitD), and in the primary and permanent teeth of children with x-linked hypophosphatemic rickets (inability to utilize vitD). What we don't know is the maternal serum circulating vitD levels during pregnancy necessary to impact the child's dental health. We propose a biological investigation of the impact of maternal circulating vitD during pregnancy and DDE in the primary tooth development. Our hypothesis is that pregnancy vitD levels influence in utero the child's primary tooth development and subsequent susceptibility to dental caries. A best test of the cause-effect of low circulating maternal vitD levels during pregnancy, enamel defects of those teeth formed in utero, and early childhood caries, would be a prospective study of mothers with monthly monitoring of vitD during pregnancy and then following the children to examine their teeth. The enamel crowns of the primary maxillary central incisors begin development about 13-15 weeks of gestation, are mostly formed by birth, and serve as a record of pregnancy events. They erupt into the oral cavity at about 1 year of age, are readily observable by 2 years, and exfoliated by age 7-8 years. We are uniquely poised to conduct a secondary analyses of our existing data resources study to assess the critical amount and/or timing of serum circulating maternal 25(OH)D during human tooth development to produce a tooth without EH. Our databases include maternal biochemistries from 12 weeks of pregnancy and monthly through delivery, and also digital images of their children's two front teeth made annually from 2 years of age using 2 levels of magnification (3x and 50x). Aim 1 is to develop an imaging standard for EH derived from a stability measure computed from the EH scores assigned to the digital images of the same teeth per child at two annual visits. We will consider both separate tooth scores and total score across teeth using 3 buccal locations on each tooth. Bayesian models for each magnification are fitted jointly so that we can estimate differences between random effects at the individual level and for magnification by time. We propose to use posterior sampling to estimate posterior quantities for these models and functionals of the posterior distributions. After testing we will have assessed whether substantive differences exist between magnifications in terms of stability over time and variability. For Aim 2 we will assess the relationship between the maternal 25(OH)D levels measured longitudinally during pregnancy and the presence of EH in the child's teeth. We will develop hierarchical Bayesian longitudinal mixed effect models for the temporal development and correlation of the exposure and outcome. The results of this study are designed to close the gap in knowledge and provide an analytical approach concerning maternal circulating serum vitD levels during pregnancy and EH in the child.